Q:
Is it possible for a black hole to "eat" an entire galaxy? If so, what
about the 1% mass rule? It would seem at some point the universe would
be nothing but black holes, thereby after succumbing to
evaporation

A:
We cannot think of a scenario where a black hole
would eat an entire galaxy. The gravitational reach of supermassive black
holes contained in the middle of galaxies is large, but not nearly large
enough for this task. Also, gravity by itself isn't enough. For example, if
the Sun suddenly turned into a black hole of the same mass, we'd continue
to orbit it without being pulled in. Of course, this wouldn't be good for
life on Earth!